A typical conveyor for conveying relatively small articles includes a frame, having a pair of spaced side rails that support a bed plate. A conveying member, such as an endless conveyor belt, is supported on the bed plate and the belt is driven by a drive spindle or pulley which is located at one end of the conveyor, while the belt is trained over an idler spindle located at the opposite end of the conveyor.
It is desirable that a conveyor include a mechanism for tensioning and tracking the conveyor belt. In certain conveyors, the belt tensioning and tracking mechanisms are combined by journaling the ends of the tensioning roll or spindle in slide blocks which are slidable relative to the conveyor frame. By adjusting the position of the slide blocks, the belt tension and tracking can be adjusted. However, in mechanisms of this type, a tracking adjustment can effect the tensioning, and vice versa, so that trained personnel are required in order to properly adjust the tension and tracking.
U.S. patent application Serial Nos. 07/731/526, filed Jul. 17, 1991, and 07/637,636, filed Jan. 4, 1991, disclose improved belt tensioning and tracking mechanisms for a conveyor. In accordance with the teachings of the aforementioned patent applications, the conveyor belt is carried by an adjustable spindle assembly, which is located at one or both ends of the conveyor frame. The spindle assembly includes a belt-supporting spindle that is journaled between a pair of side members which are mounted for sliding movement relative to the side rails of the conveyor. Tension on the belt is adjusted by a rack and pinion mechanism in which at least one rack is mounted on the conveyor frame between the side rails and extends longitudinally of the frame. An end of the rack is engaged with the spindle assembly, while a pinion is mounted transversely between the side rails and is engaged with the rack. Rotation of the pinion will move the rack longitudinally to thereby adjust the position of the spindle assembly and control the tension on the conveyor belt.
The belt tracking mechanism, as disclosed in the aforementioned patent applications, is separate from the belt tensioning mechanism. The tracking mechanism includes a pair of cam blocks, each of which is mounted to one of the side rails of the conveyor. Each cam block includes a rotatable cam or eccentric that is engaged with the corresponding side member of the spindle assembly. By individually rotating each cam, each side member of the spindle assembly can be moved longitudinally to thereby skew or track the conveyor belt.
The spindle assembly, as described in the above patent applications, also includes an articulated linkage that extends transversely between the side members of the spindle assembly. The articulate linkage provides a dual function in that it not only stabilizes or provides rigidity for the spindle assembly, but due to the articulated nature, permits the side members of the spindle assembly to be moved longitudinally relative to each other to track the belt.
The side rails of the typical conveyor are produced with certain tolerances and similarly the side members of the spindle assembly, which are preferably metal stampings, are also formed within certain tolerances. Due to a tolerance build-up it has been found that when the side members of the spindle assembly are locked relative to the side rails of the conveyor frame, the side members may not be precisely parallel, but may tend to either converge or diverge, depending on the build-up of tolerances. This not only detracts from the appearance of the conveyor, but if the side members converge, the converging side members can restrict movement of the conveyor belt causing excessive wear on the belt and possible jamming.